Structures and Bioactivities of Steroidal Saponins Isolated from the Genera Dracaena and Sansevieria

The species Dracaena and Sansevieria, that are well-known for different uses in traditional medicines and as indoor ornamental plants with air purifying property, are rich sources of bioactive secondary metabolites. In fact, a wide variety of phytochemical constituents have been isolated so far from about seventeen species. This paper has reviewed the literature of about 180 steroidal saponins, isolated from Dracaena and Sansevieria species, as a basis for further studies. Saponins are among the most characteristic metabolites isolated from the two genera. They show a great variety in structural motifs and a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-proliferative effects and, in most case, remarkable cytotoxic properties.     

Emissions and deposit properties from combustion of wood pellet with magnesium additives

This work studies the amount of gaseous and particle emissions and deposits on heat exchanger surfaces in a boiler firedwith commercially available pellets and with pellets primed with magnesium oxide and magnesium hydroxide.The combustionexperiments were performed on a residential boiler of 20 kW.Substrates placed in the heat exchanger was analysed with SEM-EDX-mapping to evaluate the chemical composition of the deposits.The results show that particle emissions(PM 2.5)using the additivesincreased by about 50%and the mass of the deposits in the flue gas heat exchanger(excluding loose fly ash)increased by about25%compared to the combustion of pellets without additives.The amount of additives was found to be eight times higher than theamount of the main alkali metals potassium(K)and sodium(Na)which leads to the assumption that the additives were overdosedand therefore caused the problems reported.The SEM analysis of the substrates placed in the flue gas heat exchanger indicate that thedeposits of sodium(Na),potassium(K),chlorine(Cl)and sulphur(S)decrease using the additives.If this was due to theexpected chemical reactions or due to the loose fly ash covering the substrates after the test,could not be determined in this study.     

Direct excitation luminescence spectroscopy of Eu(III) complexes of 1,4,7-tris(carbamoylmethyl)-1,4,7,10- tetraazacyclododecane derivatives and kinetic studies of their catalytic cleavage of an RNA analog

The macrocycles 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetrazacyclododecane (1), 1,4,7-tris[(N-ethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (2), 1,4,7-tris[(N,N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (3) and their Eu(III) complexes are prepared. Studies using direct Eu(III) excitation luminescence spectroscopy show that all three Eu(III) complexes exhibit only one predominant isomer with two bound waters under neutral to mildly basic conditions (Eu(X)(H(2)O)(2) for X = 1-3). There are no detectable ligand ionizations over the pH range 5.0-8.0 for Eu(3), 5.0-8.5 for Eu(2) or 5.0-9.5 for Eu(1). The three Eu(III) complexes show a linear dependence of second-order rate constants for the cleavage of 4-nitrophenyl-2-hydroxyethylphosphate (HpPNP) on pH in the range 6.5-8.0 for Eu(3), 7.0-8.5 for Eu(2) and 7.0-9.0 for Eu(1). This pH-rate profile is consistent with the Eu(III) complex-substrate complex being converted to the active form by loss of a proton and with Eu(III) water pK(a) values that are higher than 8.0 for Eu(3), 8.5 for Eu(2) and 9.0 for Eu(1). Inhibition studies show that Eu() binds strongly to the dianionic ligand methylphosphate (K(d) = 0.28 mM), and more weakly to diethylphosphate (K(d) = 7.5 mM), consistent with a catalytic role of the Eu(III) complexes in stabilizing the developing negative charge on the phosphorane transition state.     

Identifying Different Types of Catalysts for CO2 Reduction by Ethane through Dry Reforming and Oxidative Dehydrogenation

The recent shale gas boom combined with the requirement to reduce atmospheric CO₂ have created an opportunity for using both raw materials (shale gas and CO₂) in a single process. Shale gas is primarily made up of methane, but ethane comprises about 10 % and reserves are underutilized. Two routes have been investigated by combining ethane decomposition with CO₂ reduction to produce products of higher value. The first reaction is ethane dry reforming which produces synthesis gas (CO+H₂). The second route is oxidative dehydrogenation which produces ethylene using CO₂ as a soft oxidant. The results of this study indicate that the Pt/CeO₂ catalyst shows promise for the production of synthesis gas, while Mo₂C‐based materials preserve the C? C bond of ethane to produce ethylene. These findings are supported by density functional theory (DFT) calculations and X‐ray absorption near‐edge spectroscopy (XANES) characterization of the catalysts under in situ reaction conditions.     

Kinetic Monte Carlo study of submonolayer heteroepitaxial growth comparing Cu/Ni and Pt/Ni on Ni(100)

The surface patterns formed during submonolayer Cu/Ni and Pt/Ni heteroepitaxy upon a Ni(100) substrate have been investigated by kinetic Monte Carlo (KMC) simulations. The two-dimensional (2D) KMC simulations are based upon rate constants for a complete nearest-neighbor set of 729 uncorrelated Cu or Pt atoms and/or Ni site-to-site hopping mobilities. The rate constant activation energies are determined by classical-potential total-energy calculations using an embedded-atom method potential function from the literature. We find that diffusion of Cu atoms occurs at a faster rate and Pt atoms at a slower rate than that of Ni atoms on the flat Ni(100) surface, and the initial nucleation and growth patterns of 2D islands and the kinetic versus thermodynamic control of the growth vary as a consequence. In the temperature and deposition time regime in which we work, the Cu/Ni systems show less than random mixing, while the Pt/Ni systems show more than random mixing. The Cu/Ni system has bonding energies that result in a tendency to segregate toward subdomains of pure Ni and Cu, though kinetic effects in the epitaxy trap the development of the system at small subdomain sizes. The Pt/Ni system has bonding energies giving a tendency to intermix completely, while epitaxial kinetic effects modestly interfere with the complete mixing. The kinetically determined island morphologies under various Cu/Ni and Pt/Ni compositions and deposition rates differ substantially over time periods that are long on the deposition time scale, and therefore the island patterns can become frozen in place.     

Isophosphindole p-oxide : A reactive intermediate and its reaction as a Diels-Alder diene

2-Phenylisophosphindole 2-oxide (3) was generated as a reactive intermediate by the dehydrobromination of r-1-bromo-t-2-phenylisophosphindoline 2-oxide. The existence of 3 was confirmed by trapping with various dienophiles as the Diels-Alder adducts. The stereochemistry of the [4 + 2]π cycloaddition was found to be stereospecific giving endo products with the phosphoryl group syn to the approaching dienophile. When the dienophile was an alkyne, the cycloadduct decomposed under the reaction conditions to give β-substituted naphthalene as the final product.     

Effects of Intra-Base Pair Proton Transfer on Dissociation and Singlet Oxygenation of 9-Methyl-8-Oxoguanine−1-Methyl-Cytosine Base-Pair Radical Cations

8-Oxoguanosine is the most common oxidatively generated base damage and pairs with complementary cytidine within duplex DNA. The 8-oxoguanosine−cytidine lesion, if not recognized and removed, not only leads to G-to-T transversion mutations but renders the base pair being more vulnerable to the ionizing radiation and singlet oxygen (¹O₂) damage. Herein, reaction dynamics of a prototype Watson−Crick base pair [9MOG ⋅ 1MC]⋅⁺, consisting of 9-methyl-8-oxoguanine radical cation (9MOG⋅⁺) and 1-methylcystosine (1MC), was examined using mass spectrometry coupled with electrospray ionization. We first detected base-pair dissociation in collisions with the Xe gas, which provided insight into intra-base pair proton transfer of 9MOG⋅⁺ ⋅ 1MC [9MOG − H_N1]⋅ ⋅ [1MC+H_N3′]⁺ and subsequent non-statistical base-pair separation. We then measured the reaction of [9MOG ⋅ 1MC]⋅⁺ with ¹O₂, revealing the two most probable pathways, C5-O₂ addition and H_N7-abstraction at 9MOG. Reactions were entangled with the two forms of 9MOG radicals and base-pair structures as well as multi-configurations between open-shell radicals and ¹O₂ (that has a mixed singlet/triplet character). These were disentangled by utilizing approximately spin-projected density functional theory, coupled-cluster theory and multi-referential electronic structure modeling. The work delineated base-pair structural context effects and determined relative reactivity toward ¹O₂ as [9MOG − H]⋅>9MOG⋅⁺>[9MOG − H_N1]⋅ ⋅ [1MC+H_N3′]⁺≥9MOG⋅⁺ ⋅ 1MC.